(vii) What are the factors that affect the choice of converter circuit? [2]

(viii) What is Morgan chopper? [4]

Section – B

Q-2. Discuss pulse transformer trigger circuit. Draw its equivalent circuit. What are two functional modes, write and derive equations for e, e0, eT.A relaxation oscillator using an UJT is to be designed for triggering an SCR.

The UJT has the following data: h=0.72, IP=0.6mA, VP=18.0V, VV=1.0V, IV=2.5mA, RBB=5kW, normal leakage current with emitter open = 4.2mA. The firing frequency is 2 KHz. For c=0.04mF, compute the values of R,R1 and R2. [20]

Q-3. Discuss series and parallel operations of thyristors. Write equations for string efficiency and derating. A 3KV, 750A power electronics circuit has thyristors with 800V and 175A rating. Use a derating of 25%. Find number of thyristors in series and parallel. [20]